Al Qaeda Declares Stake in Syrian Rebellion

BEIRUT—Al Qaeda's branch in Iraq said it has merged with a Syrian rebel extremist faction, in a push by the terrorist organization to exert more influence on the Syrian rebellion and its outcome.

The declaration reflects cross-border coordination between al Qaeda in Iraq and Syria's Jabhat al Nusra, or the al Nusra Front, a force with growing battlefield clout that has been a target of U.S. efforts to isolate rebel extremists in Syria. The two groups are already closely linked; when the U.S. designated the Syrian group as...